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Protect 2 - Philips FL9.1 Technical Training Manual

Lcd tv chassis for 2009
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+33V
Protect 2 (Figure 8)
Protect 2 monitors the circuit feeding the 3.3V standby supply.
In the standby mode, the +33V supply will measure approximately 8 volts. When the set is
turned On, it will go to +33V as the power supply goes to a full power mode. Q635 regulates
the voltage feeding IC631, AL3.3V regulator.
If Q635 fails, the voltage at the emitter of Q635 would exceed the voltage of the 10 volt zener,
D407 causing it to conduct. This will cause the PROTECT 2 line to go High resulting in the
TV set turning Off.
Page 16
R662
15
Q635
D636
2.7
D660
R636
2.7
D407
10V
FIGURE 8 - PROTECT 2
R660
R663
1.8K
R664
1.8K
D659
6.8V
D637
D418
3.9V
IC631
3.3V
REG
PROTECT2
AL3.3V

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